HSCI 3013 Exercise 7
Tycho's problems with orbs
In 1588, Tycho Brahe published a new system of the world. Keeping the earth as the center of the
cosmos, the moon and the sun both revolve around the earth, as in Ptolemy's system. But all the
other planets have motions centered on the sun, and are carried around with it, in the same way
that the moon is carried around with the earth in Copernicus's system.
Question 1: Ignoring the moon, use the distances provided for Copernicus in the previous exercise
to draw the inner part of Tycho's system, with the earth in the center, the sun going around the
earth, and Mercury and Venus going around the sun. If the physical orb of the sun must be thick
enough to accommodate the orbs you have drawn for Mercury and Venus, what must its inner
and outer radii be?
Question 2: On the same diagram draw in the maximum and minimum distances for Mars. Be sure your diagram shows what happens on the opposite side of the earth from the sun. If the orbs we have drawn so far are treated as solid objects, is there anything wrong with this picture? If the orbs are treated as no more than geometrical boundaries in a continuous fluid medium, can Mars and the Sun ever collide?